Anaphylaxis Diagnosis and Management

Definition and Classification

• Anaphylaxis is a severe, life-threatening, generalized or systemic hypersensitivity reaction characterized by rapid onset and potentially fatal outcomes without appropriate intervention, according to the American Academy of Pediatrics 1
• The American College of Allergy, Asthma, and Immunology defines anaphylaxis as a severe, life-threatening, generalized or systemic hypersensitivity reaction that produces an allergic response 2, 3
• Anaphylaxis can be divided into "allergic anaphylaxis" (immune-mediated) and "non-allergic anaphylaxis" (non-immune-mediated), as stated by the American Academy of Allergy, Asthma, and Immunology 3, 4

Clinical Manifestations

• Anaphylaxis typically presents with multi-system involvement, including respiratory symptoms such as dyspnea, wheeze, bronchospasm, stridor, reduced peak expiratory flow, and hypoxemia, according to the American Heart Association 2, 5
• Cardiovascular symptoms of anaphylaxis include hypotension, tachycardia, shock, and cardiac arrest, as reported by the American Heart Association 5

Diagnostic Criteria

• The American Academy of Allergy, Asthma, and Immunology states that anaphylaxis is highly likely when any one of the following criteria is met: acute onset with skin/mucous membrane involvement PLUS respiratory compromise OR reduced blood pressure 2
• The American College of Allergy, Asthma, and Immunology also reports that two or more of the following occurring rapidly after allergen exposure indicate anaphylaxis: skin/mucous membrane involvement, respiratory compromise, reduced blood pressure, persistent gastrointestinal symptoms 2, 6

Management

• The American Academy of Pediatrics recommends first-line treatment with epinephrine (adrenaline) administered intramuscularly in the mid-outer thigh at a dose of 0.01 mg/kg (maximum 0.5 mg in adults, 0.3 mg in children) 1, 6
• The American Heart Association states that epinephrine is the cornerstone of anaphylaxis management and should not be delayed 5, 6

Prevention and Long-term Management

• The American Academy of Pediatrics recommends patient education on recognition and management of anaphylaxis, as well as referral to an allergist for comprehensive evaluation 1, 7
• The American Academy of Allergy, Asthma, and Immunology suggests prescription of epinephrine auto-injectors for at-risk patients 1, 4

Anaphylaxis Classification and Management

Introduction to Anaphylaxis Classification

• The European Academy of Allergy and Clinical Immunology (EAACI) and the World Allergy Organization (WAO) recommend abandoning the term "anaphylactoid" in favor of "anaphylaxis" for all systemic severe reactions, regardless of the mechanism 8, 9
• The current recommended term is "allergic anaphylaxis" when the reaction is mediated by an immunological mechanism (IgE, IgG, or complement activation) 8, 9
• For non-immunologically mediated reactions, the term "non-allergic anaphylaxis" should be used instead of "anaphylactoid" 8, 9

Anaphylaxis Mechanisms and Classification

• Anaphylaxis can be divided into two categories based on the mechanism: allergic (immunologically mediated) and non-allergic (non-immunologically mediated) 8, 9
• Allergic anaphylaxis is mediated by IgE, IgG, or complement activation, while non-allergic anaphylaxis involves direct mast cell activation or other non-immunological mechanisms 8, 9
• The European guidelines (EAACI, 2009) establish that the term "anaphylactoid" should be abandoned and recommend using "non-allergic anaphylaxis" 8

Clinical Implications and Management

• The distinction between mechanisms has limited relevance in acute management, as the first-line treatment is identical: epinephrine intramuscularly 0.01 mg/kg (maximum 0.5 mg in adults, 0.3 mg in children) regardless of the mechanism 8
• The clinical manifestations are indistinguishable between the two types, and the risk factors for severe reactions are the same: beta-blockers, ACE inhibitors, advanced age, and cardiovascular comorbidities 9
• Patients with beta-blockers or ACE inhibitors have a higher risk of severe anaphylaxis and reduced response to epinephrine, regardless of the immunological or non-immunological mechanism 9

Hypersensitivity Reactions as Triggers of Acute Heart‑Failure Decompensation

Mechanisms of Decompensation

Direct Myocardial Injury

• The 2022 AHA/ACC/HFSA heart‑failure guideline identifies myocarditis caused by hypersensitivity reactions as a distinct etiology of acute heart‑failure decompensation. 10

Cardiovascular Collapse from Anaphylaxis

• Anaphylaxis leads to a rapid fall in cardiac output because of reduced coronary perfusion pressure, impaired venous return, and possible coronary artery spasm from mediator release. 11
• Within minutes of severe anaphylactic shock, myocardial ischemia with electro‑cardiographic changes commonly occurs, precipitating acute decompensation in patients with underlying cardiac disease. 11
• In individuals with pre‑existing heart failure, the combined effects of hypotension, tachycardia, and heightened myocardial oxygen demand during anaphylaxis can trigger rapid decompensation even without direct myocardial injury. Evidence from allergy‑immunology studies supports this mechanism. [12][11]

Systemic Inflammatory Response

• Sepsis‑like inflammatory cascades that accompany severe hypersensitivity reactions are linked to reversible myocardial depression mediated by cytokine release. 13
• Immune‑driven infections raise metabolic demand and may cause hypoxia, both recognized precipitants of acute heart‑failure decompensation. 13

High‑Risk Populations

Patients with Pre‑Existing Cardiovascular Disease

• Patients with established heart failure should receive intramuscular epinephrine during anaphylaxis despite concerns about cardiac effects, because the life‑threatening risk of untreated anaphylaxis outweighs potential epinephrine‑related harm. 12
• This recommendation also applies to patients on β‑blockers, who have a higher risk of severe anaphylaxis and a blunted response to epinephrine. 12
• Use of ACE inhibitors or β‑blockers is associated with an increased risk of severe anaphylaxis leading to cardiovascular collapse and subsequent decompensation. 11

Clinical Recognition and Management

Diagnostic Considerations

• When assessing acute heart‑failure decompensation, clinicians should obtain a detailed history to uncover recent exposures (new medications, insect stings, allergens) that could act as hypersensitivity triggers. This recommendation is supported by both the 2022 AHA/ACC/HFSA guideline and 2013 Circulation evidence. [13][10]

Immediate Management of Anaphylaxis‑Triggered Decompensation

• Intramuscular epinephrine (0.01 mg/kg, max 0.5 mg adult, 0.3 mg child) is the first‑line treatment and must not be delayed in patients with cardiac disease. This is a Class I, Level A recommendation from allergy‑immunology guidelines. [12][14]
• Re‑dosing of epinephrine is advised for persistent or recurrent symptoms; antihistamines and corticosteroids should not replace epinephrine. 12

Heart‑Failure‑Specific Management

• Guideline‑directed heart‑failure therapy should be continued during hypersensitivity‑related decompensation unless hemodynamic instability or a specific contraindication arises, as endorsed by 2013 Circulation evidence. 13

Critical Pitfalls to Avoid

• Do not withhold epinephrine in heart‑failure patients experiencing anaphylaxis because the danger of untreated anaphylaxis exceeds potential cardiac side effects. 12
• Distinguish anaphylaxis from vasovagal reactions: anaphylaxis presents with tachycardia and cutaneous signs (urticaria, angioedema), whereas vasovagal episodes show bradycardia and lack skin manifestations. 14
• Do not discontinue ACE inhibitors or β‑blockers in stable heart‑failure patients solely due to fear of future hypersensitivity reactions; instead, ensure access to epinephrine and patient education. [12][13]